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By MoonShadow - 13 Years Ago
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I have a rather old mechanical oil pressure gauge in my dash. When I started my new engine I ran it off and on for several days while making adjustments (turns out I had a bad carb). Oil pressure on an external mechanical gauge stayed at 60-80 until warmed up then dropped to around 30lbs. Not bad. Today I connected the gauge in the dash and went for a drive. I immediately noticed the oil pressure reading very low 5-0lbs when stopped. Revving the engine in neutral would bring it up a bit but not over 20. Engine is quiet and running well. Thats why I was wondering if those mechanical gauges ever go bad. I'll hook the other gauge up at the dash tomorrow and see what it reads. I figure using the same line as the current dash gauge should tell me if its in the line. Anyway, it starts and runs and shifts and all that stuff. Just have to seal up a couple exhaust flange leaks and sort out the gauges! MoonShadow Lives! Chuck
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By Glen Henderson - 13 Years Ago
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Congrats Chuck on rolling again, I know that its been a long project. I never had one quit reading, but I have had cheap ones spring a leak.
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By paul2748 - 13 Years Ago
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When I connect a mechanical oil pressure gauge, I always turn the engine over to get the oil flowing through the line before connecting to the gauge. Could you have air trapped thereby giving you a false reading?
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By Talkwrench - 13 Years Ago
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never thought of that..? trapped air, never seen fitting instuctions mention doing it, well there you go, i'll look into ..
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By bergmanj - 13 Years Ago
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Trapped air can be a good thing: It can help "cusion" oil pump pulsations which will tend to fatigue the inners of the pressure guage. The air will not change the guage's ability to read oil pressure, as the air is compressed to that same pressure and will "telegraph" the correct oil pressure into the guage. Regards, JLB
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By Don Woodruff - 13 Years Ago
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Pressure is pressure whether transmitted by oil or air. You may have a bad gague. Can you plumb it into an air pressure source and cycle it with a second gague to verify it?
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By MoonShadow - 13 Years Ago
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My plan today is to add a T at the block and install a second mechanical gauge and see what the difference is. Will post results later. Chuck
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By MoonShadow - 13 Years Ago
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Ok it rained all day so make that my plan for tomorrow. Chuck
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By mctim64 - 13 Years Ago
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If the gauge checks out look at the bypass on the pump. Might be stuck open. Does the pressure still read high when cold?
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By MoonShadow - 13 Years Ago
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Yesterday when I started the engine cold it had about 40lbs. After warming up it was hovering around the 0. The other gauge, before I removed it, was reading 60-80 cold and 20-30 hot idle. The difference is about 20lbs lower. Thats why I'm leaning towards a gauge or line problem. The oil pump is a brand new gearotor type. Its raining again today so I'll have to wait until later to hook up both gauges. I have more tinkering to do anyway. I have to move the wires one spot on the distributor to get more accurate timing. Its at 12deg but is also against the head bolt. Both of my 600 Holleys need rebuilt to work and I still have a pesky exhaust leak at both tailpipe flanges. I'm going to try double gaskets on them. Its so hard to believe that with a 28x26 garage I still have to work outside! I think I need to get rid of more stuff. Chuck
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By MoonShadow - 13 Years Ago
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I tried the two gauge hookup today. The second reads a bit higher but still drops to about 5lbs after warmup. Perhaps it is a bypass blocked open. I didn't put the bottom end togather on this one so I know its right. (good machinest) Should I change the oil filter to see if that bypass is the problem? Chuck
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By Hoosier Hurricane - 13 Years Ago
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Chuck: Your initial post said you had carb problems. Did it flood? If so, you may have diluted the oil with gasoline. Does the oil smell of gasoline? What weight oil are you using?
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By MoonShadow - 13 Years Ago
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No flooding. I had a couple of old Holleys that just wouldn't adjust properly. Both need rebuilt. The break in oil is still in the engine with no smell of gas. The scary thing is this is the same engine that lost oil pressure 2 years ago. That was a bad main bearing. Everything was rechecked and machined as needed to bring it back. Bored to standard 292 with new Isky cam and lifters. My friend at the machine shop put the short block together for me so I'm sure all the clearances are correct. (this time). I hope something is holding the bypass valve a little open and causing the problem. When the pressure is low it doesn't respond well if I rev the motor. Only goes up a little. I used a new gearotor oil pump that I had on the shelf. Didn't want to take a chance on the old pump. This is frustrating!! Chuck
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By Hoosier Hurricane - 13 Years Ago
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Chuck: Have you resolved your oil pressure problem yet? I had a couple of things you can think about. You say the oil pump was stored on the shelf for a long time. Maybe the relief valve stuck closed in its bore, causing the 70-80# pressure initially. Then, as it warmed and was lubricated some, it opened to the 40# level and stuck there. Then, as the oil warmed, the pressure dropped because the relief valve was stuck open. Check the relief valve for free movement as others have suggested. Another thing that happened on my race car this summer. I had been fighting low oil pressure early in the season, and finally got it right. 60-70# on startup, 40 at warm idle, 60 on the track. One day I started it and had 45, and thought, "oh no, here we go again". Had a small oil leak on the lower left side, rear of engine. I found the nut for the compression grommet on the inlet pipe was not very tight. Tightened it, and pressure was back to where it had been. Apparently sucking air into the pump.
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By MoonShadow - 13 Years Ago
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Thanks John. I plan to take the relief valve apart and check it. Problem is I wont be able to get to it until spring. We are setting out on a business trip this week and the car is going into storage. When I first started to prelube the engine it wasn't bringing up much pressure. Had a long wait to get pressure to the passenger side. I found that the rubber seal that fits into the oil pump had a small leak. Replaced it and the oil flow came right up. I'll recheck all the seals on the pickup when I take it down. I also plan to change the oil filter at that time. Should I take out the break in oil while I'm at it? I really think the problem will be in the pressure relief valve. Scary thing is this is exactly like the problem I had with this engine 2 years ago when it lost a main bearing shortly after a complete rebuild. I know the bottom end was put together correctly this time as my machinist did it for me. He is as precise a dude as Ted! Chuck
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By Hoosier Hurricane - 13 Years Ago
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Chuck: Maybe I need to see a shrink to make me stop thinking about you. My latest thought to keep you busy is this: are you using the same pickup tube that was in the previous engine with oiling problems? How about a crack in the tube above the oil level, allowing air to be drawn in instead of pure oil? Checking the oil for aeration and bubbles after running the engine would point to air entering the oil system.
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By John Mummert - 13 Years Ago
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Chuck, you say you had a new gerotor pump on the shelf. If the body is cast iron it is likely a Dynagear pump. I had lots of problems with those pumps. They had great oil pressure cold but it dropped off quickly as the oil heated up. They were made until 2005, more or less.
Dyna is no longer in business.
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By MoonShadow - 13 Years Ago
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Thanks for the input John. My pump is the all aluminum body not cast iron. Did they ever pinpoint a reason for the drop in pressure? Chuck
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By MoonShadow - 13 Years Ago
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Finally back from the business trip. I changed the oil filter today and the oil pressure came up. It still seems a bit low but it is a stock pump. Starts cold at 40 idles hot at about 15. Also when I rev the engine the oil pressure goes up (wasn't happening before). So I guess the WIX filter had a bad relief valve in it. Does anyone have the high pressure spring kit for the oil pump? Or is there a trick to changing the relief spring to increase pressure? It seems we used to stretch them but I can't remember the details. Engine sounds very good and runs well. I have to get the final tune done on it and see what it will do. Question, does the MSD distributor operate on full vacume or ported? There was some discussion about it at the shop today. Chuck
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By slumlord444 - 13 Years Ago
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You can shim the spring with flat washers. Go slowly. I over did it once and blew the gasket out of the filter.
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By YellowWing - 13 Years Ago
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There has been some debate on here about the ported versus full vacuum as well. The consensus seems to be to use ported vacuum in most cases. This is also what MSD calls for. I set my MSD up with ported vac. and it is working well. If yo use full vacuum be aware that you will end up with near full vacuum advance at idle. Mike
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By MoonShadow - 13 Years Ago
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Thanks for the response on shimming the spring. I think when I was young and new everthing a frined told me about stretching the spring. Washers make much more sense. How much do you think you shimmed it out? For the MSD, the shop in question was working on a scrub cumerror. Wouldn't run at all well on ported vacume but cleaned right up on full. Thats what made me wonder. I'll dig out the paper work later and see what MSD says. Thanks! Chuck
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By YellowWing - 13 Years Ago
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In case you don't have the instructions here is the quote from MSD. Vacuum Advance: The vacuum advance will advance the timing up to 10° during partial throttle driving (with 15 lbs of vacuum). The vacuum line should be routed to a ported vacuum outlet above the throttle plates. And a link to them. Mike http://www.msdignition.com/uploadedFiles/MSDIgnitioncom/Products/distributors/8383_instructions.pdf
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By MoonShadow - 13 Years Ago
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Thanks Mike. That is how I have it setup now. Chuck
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By slumlord444 - 13 Years Ago
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I woould put a couple and try it. As I said, go slowly because too much pressure is not good either.
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By Hoosier Hurricane - 13 Years Ago
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Chuck: Keep in mind that shimming the spring will only increase the maximum oil pressure, will make no difference in the idle and low speed pressure.
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